The present invention relates to brake lining material. More particularly, the present invention relates to a method and apparatus for the manufacture of the brake lining material used in various braking applications.
The automotive industry, including both cars and trucks, and the manufacturing community utilize drum brakes for their braking systems. The drum brake is known as an internal expansion brake and it includes a brake drum having an internal generally circular cylindrical braking surface. The brake drum normally rotates with the vehicles wheel or with a rotating component of a machine tool. One or more brake shoes are located within the center of the circular cylindrical braking surface. The brake shoes have a frame onto which is attached a sacrificial brake lining which is shaped to mate with the braking surface of the brake drum. The rotating wheel or component is stopped by radially extending the brake shoe such that the sacrificial lining frictionally engages the braking surface on the brake drum. The energy of the rotating wheel or component is dissipated by the frictional engagement between the braking surface of the brake drum and the brake lining on the brake shoe. Over time and use, the sacrificial lining is worn away and has to be replaced in order for the braking system to continue to function. Normally this involves the replacement of the brake shoe and the resurfacing of the braking surface of the brake drum. The worn brake shoe is not discarded, it is sent back to a rebuilder who removes the old lining from the frame and replaces it with a new lining. The brake linings generally are circular cylindrical segments which may be bonded, riveted or otherwise attached to the frame of the brake shoe.
The material for the brake lining is normally supplied in a flat rectangular shape. The material is either of the proper dimensions to form the lining for the brake shoe or the flat rectangular sheet of material is cut into one or more rectangular pieces to form the brake lining material. The final sized flat rectangular piece of brake lining material is then formed into a curved shape and attached to the frame of the brake shoe by bonding methods, riveting or the like.
Conventionally, the flat rectangular shape of brake lining material is formed in a press having a mold of the proper dimensions for the brake lining material. A pellet of uncured brake lining material is inserted into the mold and a punch is pressed against the pellet of material forcing it to fill the mold and thus take on the desired flat rectangular shape. The punch is continuously moved toward the open mold until it contacts a stop which is usually the top surface of the mold. Once the material has been fully cured, the punch retracts and ejector pins push the completed brake lining material out of the mold. In order to ensure that a complete fill of the mold is obtained, the pellet is sized to be larger than the volume of the mold. Typically, the pellet is 5% larger than the volume of the mold. This excess material is formed as molding flash which must be trimmed from the finished sheet of brake lining material and then discarded.
Thus, the conventional methods of manufacturing a sheet of brake lining material suffer from two disadvantages. First, it is necessary to build into the process a 5% waste factor due to the need to completely fill the mold. Second, the 5% waste ends up as mold flash which requires an additional trimming operation before the material can be used.
The continued development of manufacturing processes for the brake lining materials has been directed towards method of eliminating the excess material, the accompanying scrap and the additional manufacturing operation required because of the excess material.
The present invention provides the art with a method and apparatus for producing a sheet of brake lining material without using excess material and thus eliminating the accompanying scrap and the additional manufacturing operation. The present invention utilizes a stepped mold base around which is disposed a mold frame. The mold frame is movable with respect to the mold base. A precise amount of brake lining material is placed within the mold frame which is then covered. The forming press then engages the mold and presses against the mold to move the mold frame and layer with respect to the base until a predetermined pressure is reached and not to a predetermined stop. The positive pressure molding is permitted because of the design of the mold where the mold frame is free to move with respect to the base. Thus, the thickness of the molded sheet will be dictated by the amount of material in the preformed pellet with the positive pressure molding ensuring complete fill of the mold.